000
WTPA41 PHFO 310255
TCDCP1
TROPICAL STORM LANA DISCUSSION NUMBER 3
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062009
ISSUED BY NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM HST THU JUL 30 2009
LANA HAS CONTINUED TO INTENSIFY THIS AFTERNOON WITH A WELL-DEFINED
SPIRAL BAND PATTERN PRESENT ON SATELLITE IMAGERY. IN ADDITION...
AN AQUA MICROWAVE PASS AT 2240 UTC SHOWS SIGNIFICANT INNER-CORE
STRUCTURE WITH A BROKEN RING OF CONVECTION AROUND THE STORM CENTER.
DVORAK ESTIMATES AT 0000 UTC WERE 45 KT FROM TAFB/CIMSS...AND SINCE
THAT TIME...THE CYCLONE IS BECOMING BETTER-ORGANIZED WITH
INCREASING CONVECTION ON THE WESTERN SIDE. THE INITIAL INTENSITY
IS RAISED TO 50 KT...AND THIS COULD BE CONSERVATIVE BASED ON THE
MICROWAVE AND RECENT INFRARED SATELLITE DATA.
VERTICAL WIND SHEAR IS EXPECTED TO BE LOW FOR THE NEXT DAY OR SO AS
LANA REMAINS UNDER THE INFLUENCE OF THE SOUTHWESTERN PORTION OF AN
UPPER HIGH. THIS LIGHT SHEAR ALONG WITH WARM SSTS SHOULD ALLOW
STRENGTHENING UNTIL THE CYCLONE INTERACTS WITH A LARGE MIDDLE- TO
UPPER-LEVEL LOW CURRENTLY SEEN OVER HAWAII. THIS UPPER-LOW SHOULD
START TO INCREASE THE SHEAR OVER THE SYSTEM IN A COUPLE OF DAYS AND
SIGNIFICANTLY WEAKEN LANA BY THE END OF THE FORECAST PERIOD.
THE OFFICIAL NHC FORECAST IS CLOSE TO...BUT A LITTLE HIGHER
THAN...THE MODEL CONSENSUS INITIALLY...AND IS CLOSE TO THE SHIPS
MODEL IN 3-5 DAYS.
THE BEST ESTIMATE OF INITIAL MOTION IS 285/17. A MID-LEVEL HIGH
LOCATED TO THE NORTHEAST OF HAWAII SHOULD PROVIDE THE STEERING
FOR LANA DURING THE NEXT SEVERAL DAYS...KEEPING THE STORM
ON A WEST OR WEST-NORTHWEST HEADING. ALL OF THE GLOBAL MODELS
WEAKEN THE STRONG MIDDLE-TO UPPER-LEVEL LOW NEAR HAWAII AND SHOW
ENOUGH RIDGING TO ALLOW THE STORM TO REMAIN SOUTH OF THE HAWAIIAN
ISLANDS. THERE HAS BEEN A NOTICEABLE NORTHWARD SHIFT OF THE STORM
TRACK IN THE RECENT GUIDANCE FROM THE GFS/GFDL/HWRF MODELS. THIS
CHANGE COULD BE ATTRIBUTED TO THE GFS MODEL HAVING A MORE
REALISTIC REPRESENTATION OF THE STORM THAN EARLIER...ALTHOUGH IT IS
DIFFICULT TO TELL THE EXACT REASON AT THIS TIME. THE OFFICIAL NHC
FORECAST IS SHIFTED TO THE NORTH FROM THE PREVIOUS ONE...BUT STILL
LIES SOUTH OF THE MODEL CONSENSUS...SIGNIFICANTLY SO AT THE
LONG-RANGE.
FORECAST POSITIONS AND MAX WINDS
INITIAL 31/0300Z 12.8N 143.1W 50 KT
12HR VT 31/1200Z 13.2N 145.5W 60 KT
24HR VT 01/0000Z 13.7N 148.4W 65 KT
36HR VT 01/1200Z 14.2N 151.2W 65 KT
48HR VT 02/0000Z 14.6N 153.9W 60 KT
72HR VT 03/0000Z 15.2N 159.5W 50 KT
96HR VT 04/0000Z 16.0N 165.5W 35 KT
120HR VT 05/0000Z 16.5N 171.0W 25 KT...REMNANT LOW
$$
FORECASTER BLAKE